Injection of a liquid such as a drug into a human patient or an agriculture animal is performed in a number of ways. One of the easiest methods for drug delivery is through the skin which is the outermost protective layer of the body. It is composed of the epidermis, including the stratum corneum, the stratum granulosum, the stratum spinosum, and the stratum basale, and the dermis, containing, among other things, the capillary layer. The stratum corneum is a tough, scaly layer made of dead cell tissue. It extends around 10-20 microns from the skin surface and has no blood supply. Because of the density of this layer of cells, moving compounds across the skin, either into or out of the body, can be difficult.
The current technology for delivering local pharmaceuticals through the skin includes methods that use needles or other skin piercing devices. Invasive procedures, such as use of needles or lances, effectively overcome the barrier function of the stratum corneum. However, these methods suffer from several major disadvantages: local skin damage, bleeding, and risk of infection at the injection site, and creation of contaminated needles or lances that must be disposed. Further, when these devices are used to inject drugs in agriculture animals, the needles break off from time to time and remain embedded in the animal.
Needleless injection devices have been proposed to overcome the problems associated with needles, but the proposed devices present different problems. For example, some needleless injection devices rely on spring actuators that offer limited control. Others use solenoids, compressed air or hydraulic actuators also offer limited control.